Adjustable brush arm mount for potentiometers



R. G. HENLEY June 21, 1966 ADJUSTABLE BRUSH ARM MOUNT FOR POTENTIOMETERS Filed April 24, 1965 mm n R m Y N W N E 1 H mm a WN m G O R L ATTORNEYS United States Patent O 3,257,634 ADJUSTABLE BRUSH ARM MOUNT FOR POTENTIOMETERS Roger G. Henley, Littleton, Mass., assignor to Ace Electronics Associates, Inc., a corporation of Massachusetts Filed Apr. 24, 1963, Ser. No. 275,454 i 7 Claims. (Cl. 33S-135) Vance element and traverse its length on rotation of said shaft, whereby a voltage related 'to the angular position of the shaft is derived from the resistanceelement by means of the brush.

In certain applications a number of rotary potentiome-4 ters or rheostats are ganged together for simultaneous and unison rotation of their several shafts. In' these :applications it is usually important for the brushes to be angularly phased on their respective shafts relative to one another, so ,that the output voltages derived from the ganged units all bear a specific relationship to each other. Usually the shafts lare designed so that they can be ganged to each other in only one 'angular relationship. Therefore to obtain a desired output voltage phase -relationship it is necessary to adjust the angular relationship of either the brush or the resistance element relative to la reference setting of the shaft.

The present invention is concerned with accomplishing this phasing adjustment by means of adju-sting the brush relative to the shaft, and this is generally accomplished herein by providing for an angularly adjustable brush `arm mounting on the shaft. Angularly adjustable brush arm mountings :are of course known in the art, however theyare generally diiicult to use, particularly in the confined space of miniature rotary potentiometers The prior art approaches usually rely upon a bifurcated mount ladapted to straddle over the rotary shaft. One prior mode of clamping 'the mount is effected by means of a clamping screw which connects the two tines of the bifurcated mount along a line transverse to an axial plane of the rotary shaft to tighten said tines upon said shaft. Another prior mode of clamping the bifurcated mount is to use the resilient spring force of the bifurcated mount, forcing the tines apart when it is desired to effect a relative adjustment between the mount and the shaft.

As distinguished from the teachings of the prior art, the present invention effects a clamping of the adjustable brush arm mount by means of a clamping force exerted parallel to the axis of the rotary shaft. To this end, the rotary shaft is` provided with two axially spaced bearing points, and the brush arm assembly including the mount is located between these bearing points. A clamping screw extending along Aa line parallel with the rotary shaft axis is carried by one of said bearing points, and said screw functions to clamp said assembly between it and the other bearing point. Due to its raxial orientation, the clamping screw is readily accessible rand can be very readily loosened by a tool inserted along the axis of the shaft, whereupon the angular relationship of the mount and brush arm assembly to the rotary shaft can be adjusted with great precision and the clamp again tightened to retain the parts in adjusted relationship.

It is accordingly one object of the present invention Patented June 21, 1966 to provide an angularly adjustable brush arm mounting assembly forrotary potentiometers or rheostats.

Another object of the present invention is to provide a brush arm mounting assembly for rotary potentiometers or rheostats, wherein the assembly is angularly adjustably mounted on the rotary shaft of the potentiometer or rheostat.

Another object of the present invention is to provide an angularly adjustable brush arm mounting assembly for rotary potentiometers or rheostats, wherein the assembly is releasably clamped to -and angularly `adjustable relative to the rotary shaft of the unit by means of a clamp arranged axially of the rotary shaft.

Other objects rand ladvantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of one exemplary specific embodiment of the present invention, had in conjunction with the accompanying drawings, in which like numerals refer to like or corresponding parts, and wherein:

FIG. l -is a front elevation View of an open front rotary potentiometer embodying the present invention;

FIG. 2 is la cross-sectional view of the potentiometer, taken along line 2 2 of FIG. 1;

FIG. 3 is an enlarged, fragmentary, cross-sectional view of that portion of the potentiometer including the adjustable brush arm mounting assembly;

FIGS. 4-6 are elevation views of three parts of said mounting assembly taken separately; and

FIG. 7 is a perspective view of another part of said assembly taken separately.

The potentiometer shown in FIGS. l and 2 comprises la cup-like housing 10, usually molded from an insulating plastic. A resistance card 12 is mounted on the inside annular surface 11 of cup 10. The resistance card 12 is a conventionalelement well known in the art, and therefore is not shown in detail. It comprises a central core of insulation material, usually fabricated from liber or plastic, about which'a suitable resistance wire is wound in helical fashion, to provide anellongate resistance element extending between terminals 12a and 12b at each end of the card. A shaft 13 is rotationally mounted on the central axis of the cup 10 by means of a ball bear-ing assembly 14, and is retained against axial m-ovement by retaining washers 15.

An angular-ly .adjustable rotary brush arm and mount- Iing assembly is generally indicated by the numeral 16, and is mounted upon the shaft 13 for rotary movement therewith, yand for angular adjustment relative thereto. The mounting assembly comprises an annular insulating sleeve or bushing 17 formed with a forward ilange 18. A' conductive brush arm 19, formed with an annular opening 19a is telescoped over the bushing 17 and located against the flange 18. This brush arm includes a radially extending arm portion 19b, terminating in a turned flange 20, upon which the resilient wire brush 21 is secured by soldering or welding. Brush 21 terminates in a contact portion 22.

An annular conductive slip ring 23 is also telescoped over the insulating bushing 17 and is in electrical contact engagement with brush arm 19. An annular groove 24 is defined about the outside surface of ring 23.

The bushing 17, brush arm 19, and slip ring 23 constitute a unitized subassembly. To this end, the brush `arm :and slip ring may either be press tted onto the bushing 17, or they may be cemented thereto. To `insure good and permanent electrical contact between the contacting surfaces of the brush :arm and the slip ring, the-se two elements may be welded or soldered together.

The foregoing subassembly is mounted on the shaft 13 by slida-bly telescoping the annular `bushing 17 thereover.

This subassembly is retained in axial position on shaft 13 by means of two retaining rings 25 and 28. Retaining ring 25 is a split ring fitted in the circumferential groove 26 in shaft 13, and is preferably preassembled onto the shaft before the shaft is mounted in the cup 10. Retaining ring 28 is assembled to the shaft 13 and fitted in the circumferential groove 27 in shaft 13 after the subassembly of bushing 17, brush arm 19, and slip ring 23 is mounted in position, andthe surface of this retaining ring is thereby juxtaposed to the ange 18 on the insulating bushing 17. Retaining ring 28 carries a threaded clamping screw 29 seated in threaded aperture 30. The clamping screw is oriented along a line substantially parallel with the axis of the shaft 13. With the brush arm mounting .assembly 16 thus located on shaft 13, tightening of the clamping screw 29 against bushing 17 exerts an axial clamping force on the assembly between the two retaining rings 25 and 28. An inherent resilient circumferential clamping yforce of split ring v25 restrains it against rotation relative to shaft 13. Thus, the axial clamping action of screw 2,9 against ring 2'5 brings all the parts into firm frictional engagement to prevent the assembly from rotating relative to shaft 13. Alternatively, the axial separational force between the two retaining rings 25 and 28 effected by the force of screw 29 would effect the same clamping action even if neither retaining ring were frictionally fitted into its groove. In addition, this clamping action is enhanced by the off-axis location of screw 2-9, which produces a canting force on the ring 2S and bushing 17 to further bind them `frictionally to the shaft 13. Obviously, relative angular adjustment between the brush arm mounting assembly and .shaft 13 can be readily effected by merely loosening screw 29, rotating the assembly relative to shaft 13, and then 4retightening the screw 29.

Aperture 31 in retaining ring 28, whereby the ring is mounted on shaft 13, has a keyhole form. The smaller or semicircular portion 33 has as its center the overall center of the ring 2S, and has a diameter about equal to that of the groove 27. The larger and nearly circular portion 32 has a diameter slightly larger than that of shaft 13, so it can readily telescope thereover. This portion of the aperture 31 is positioned eccentrically on the ring 28. Thus, the ring 28 is applied over the shaft by means of the larger diameter portion of aperture 31 until it is located adjacent groove 27, where-upon the ring is shifted transversely to fit the smaller diameter portion of aperture 31 into the groove 27.

Referring to FIG. l, it will be seen that with the brush arm and its mounting assembly positioned on shaft 13, brush 21 is caused to contact the surface of resistor 12. Thus, on rotation of shaft 13, brush 21 is caused to traverse` along the length of the resistor, thereby .tapping a portion of the voltage applied to terminals 12a and 12b, depending on the position of Contact 22 on the resistor 12. This tapped voltage is obtained as an output of the potentiometer through slip ring =24 and a slip ring contact structure to be now described.

The base of the housing cup 410 is formed with an internal boss 34, on which is mounted an insulation support ring 35. At area 39 in ring 35 a U-shaped resilient wire slip ring contact structure` 3S is mounted. Contact structure A38 passes through ring -35 and its base portion is cemented thereto. The two legs resiliently straddle the slip ring 24 and ride in the annular channel 24 formed therein.

A Wire lead 4t? is soldered or welded to the base of the U-shaped slip ring contacter '38 and connects to one of the external terminals 50 mounted on top of the housing 10. Wire leads 41 and 42 also connect the terminals 12a and 12b of the resistor 12 to respective external terminals 56 located on .top of housing 1b. Thus :the standard potentiometer connections can be made to the unit through external terminals 50.

It is also frequently desired to locate one or more fixed taps along the resistor element. Such is shown at 37, where a contact is made to resistor 112 by means of resilient tap 36 mounted in insulation ring 35 in the same Way as the slip ring contacter 3S. A `wire lead 43 also connects this tap 36 .to one of the external terminals 50 on housing 10.

The potentiometer unit herein shown and described is intended to `function as one of a group of similar units axially .ganged together `for unison operation. To this end, the open end rim of the housing cup `10 is internally annularly stepped at 44, `and the bottom external rim of the cup is exteriorly stepped at 45, so that successive housings can be mated one to the next. Various known expedients (not shown) can be employed to retain the cups in assem- -bled relationship. dn order to couple the rotary shafts 13 of successive potentiometer units, one end of each shaft is slottedat 46, and the opposite end .is tongued lat 47, whereby the series of ganged shafts are rotated in unison. lt is particularly in this ganged environment that the relative phasing of the brush arms of the several potentiometers is important; and from the lforegoing description of the brush arm mounting assembly 16, it will be appreciated that this phasing can be readily accomplished by loosening clamping screw `29, adjusting the mounting assembly and its brush to a desired angular phase with relation to shaft 13, and .then retightening screw 29 to clamp the mounting assembly in the adjusted angular relation-` ship to shaft 13.

The `foregoing detailed description of one specific embodiment of the present invention is presented merely for purposes of illustration to'enable` a complete understanding thereof. It is apparent that numerous modifications and variations could be effected. Accordingly `it is not intended that the present invention be construed as limited to this embodiment, and those variations, modifications and alterations ywhich are embraced by the spirit and scope of `the appended claims are contemplated as within the purview of the present invention.

What is claimed is:

1. A potentiometer or rheostat comprising a housing, a resistance element supported by said housing, a shaft rotationally supported by said housing, a brush arm mounting yassembly supported by said shaft and rotatable therewith, and a brush carried by said assembly contacting said Iresistance element and adapted to traverse the same on rotation of said shaft, said 4brush arm mounting assembly comprising a bearing means carried shaft and projecting outwardly therefrom and restrained against axial movement therealong, a brush mounting arm means rotationally mounted on said shaft, and clamp means for forcing said brush mounting arm means axially along said shaft and against said bearing means, said clamp means comprising a second bearing means carried `by said shaft and projecting outwardly therefrom and spaced axially along said shaft from the first-mentioned bearing means and being restrained against axial movement along said shaft, and a screw carried by said second bearing means for forcing said brush mounting arm means axially along said shaft and against said fmt-mentioned bearing means, whereby said arm means may be moved angularly relative to said shaft on loosening of said screw and restrained against said angular movement by tightening of said screw.

2. A potentiometer or rheostat as set forth in claim 1, wherein said second bearing'means is a collar removably mounted in a peripheral groove in said shaft.

3. In combination, a shaft having two axially spaced peripheral grooves formed therein, a first peripherally projecting collar mounted in one of said grooves and restrained against movement relative to said shaft, a second peripherally projecting collar mounted in the other of said grooves and restrained against axial movement along said shaft, a screw carried by a threaded aperture in one of said collars and extending generally axially along said shaft,

by said and an adjustable `means rotationally mounted on said shaft between said two collars and having a portion juxta posed to said t'hreaded aperture, whereby the threading of said screw in said aperture forces said means in an axial direction along said shaft into engagement with the other of said collars to fix said means in a desired adjusted angular relationship tosaid shaft.

4. In the combination as set forth in claim 3, said screw being carried by said second collar, and said second collar having a key hole aperture therein having one portion of greater dimension than the external dimension of said shaft and another portion of lesser dimension and adapted to seat in one of said grooves.

5. A potentiometer or rheostat comprising a housing, a resistance element supported by said housing, a shaft rotationally supported by said housing, a brush arm mounting assembly supported by said shaft and rotatable therewith, and a brush carried by said assembly contacting said resistance element and adapted to traverse the same on rotation of said shaft, said brush arm mounting assembly comprising a rst peripherally projecting collar mounted on said shaft in a first groove formed in said shaft and being restrained against movement relative t-o said shaft, a .second peripherally projecting collar mounted on said shaft 1n spaced relation to said rst collar in a second groove formed in said shaft and being restrained against axial movement along said shaft, a screw carried by a threaded aperture in one of said collars and extending generally axially along said shaft, and a brush mounting ar-m means rotationally mounted on said shaft between said two collars and having a portion juxtaposed to said threaded aperture, Whereby the threading of said screw in said aperture forces said means in an axial direction along said shaft into engagement with the other of said collars to fix said means in a desired adjusted angular relationship `to said shaft.

6. A potentiometer or rheostat as set forth in claim 5, said screw being carried by said second collar, and said second collar having a key hole aperture therein having one portion of greater dimension than the external dimension of said shaft and another portion of lesser dimension and adapted to seat in one of said grooves.

7. A potentiometer or rheostat as set forth in claim 5, wherein said brush mounting arm means comprises an insulation bushing telescoped-over said shaft, a brush mounting ar-m seated over said bushing, and a slip ring seated over sai-d bushing and in electrical contact with said br-ush mounting arm.

References Cited by the Examiner UNITED STATES PATENTS 205,291 6/ 1878 Neisser 248-124 1,428,596 9/ 1922 Kruger 287-52.02 1,669,687 5/1928 Adams et al. 338-,135 2,204,623 6/1940 Ruben 338--168 X 2,738,405 3/1-956 Jorgensen et al 338-135 ANTHONY BARTIS, Acting Primary Examiner. 

1. A POTENTIOMETER OR RHEOSTAT COMPRISING A HOUSING, A RESISTANCE ELEMENT SUPPORTED BY SAID HOUSING, A SHAFT ROTATIONALLY SUPPORTED BY SAID HOSUIG, A BRUSH ARM MOUNTING ASSEMBLY SUPPORTED BY SAID SHAFT AND ROTATABLE THEREWITH, AND A BRUSH CARRIED BY SAID ASSEMBLY CONTACTING SAID RESISTANCE ELEMENT AND ADAPTED TO TRAVERSE THE SAME ON ROTATION OF SAID SHAFT, SAID BRUSH ARM MOUNTING ASSEMBLY COMPRISING A BEARING MEANS CARRIED BY SAID SHAFT AND PROJECTING OUTWARDLY THEREFROM AND RESTRAINED AGAINST AXIAL MOVEMENT THEREALONG, A BRUSH MOUNTING ARM MEANS ROTATIONALLY MOUNTED ON SAID SHAFT, AND CLAMP MEANS FOR FORCING SAID BRUSH MOUNTING ARM MEANS AXIALLY ALONG SAID SHAFT AND AGAINST SAID BEARING MEANS, SAID CLAMP MEANS COMPRISING A SECOND BEARING MEANS CARRIED BY SAID SHAFT AND PROJECTING OUTWARDLY THEREON AND SPACED AXIALLY ALONG SAID SHAFT FROM THE FIRST-MENTIONED BEARING MEANS AND BEING RESTRAINED AGAINST AXIAL MOVEMENT ALONG SAID SHAFT, AND A SCREW CARRIED BY SAID SECOND BEARING MEANS FOR FORCING SAID BRUSH MOUNTING ARM MEANS AXIALLY ALONG SAID SHAFT AND AGAINST SAID FIRST-MENTIONED BEARING MEANS, WHEREBY SAIF ARM MEANS MAY BE MOVED ANGULARLY RELATIVE TO SAID SHAFT ON LOOSENING OF SAID SCREW AND RESTRAINED AGAINST SAID ANGULAR MOVEMENT BY TIGHTENING OF SAID SCREW. 